I have been re-reading Macbeth (my daughter is studying the play as a set text), marvelling at its economy, plotting and intensity. I won't be the first person to say that it feels like a play written in a few weeks.

Shakespeare always seems to speak to one's latest preoccupations. For me, the Porter's speech, in act two, scene three – where a minor character delivers a comic soliloquy with little direct relation to the unfolding tragedy – makes an apt commentary on the place of ephemera in our literature.

Shakespeare's England is remote enough, but there are parallels with our own time. For one thing, just as we sometimes seem to be drowning in the printed word, so Elizabethan and Jacobean society witnessed an explosion of ephemeral publications: broadsheets, squibs, pamphlets, flyers and folios. Most of these are now forgotten as (presumably) most blogs, tweets and texts also will be.

But every now and again – and the Porter's speech is an example – you can see Shakespeare exploiting mundane local references for dramatic effect. It's as if he has laid aside his Holinshed or Plutarch and picked up a contemporary tabloid.

So, in Macbeth, a highly topical play, we find the Porter riffing on the keeping of Hell Gate and checking the souls of the damned. He opens by referring to "a farmer, that hang'd himself on the expectation of plenty" (clearly an allusion to market conditions) and then, more famously, to "an equivocator". This is almost certainly a reference to the Jesuit traitor Father Henry Garnet, who had been cruelly executed in the aftermath of the Gunpowder Plot.

Next, there's a jibe against "English tailors" cheating their customers. According to my Arden edition, this is a very old joke. Presumably, it would raise a laugh in the Pit, which is where the Porter was directing his speech; a moment of light relief after the horrors of the murder scene.

Shakespeare seems to understand that he has pulled off a theatrical coup here. Famously, he concludes the speech with "I pray you: remember the Porter".

As a scene, it punctuates the drama in the aftermath of Duncan's murder. As a text, it hints at the subcurrent of popular culture that flows beneath our greatest literature.

The world wide web is still so new that poetry, fiction, and drama of all genres are adjusting to the dynamic interplay of high and low culture. That, for me, is one lesson suggested by the Fifty Shades of Gray phenomenon. Those books are still global bestsellers. Who will read, still less remember, them 10 years from now?